The delta variant of the coronavirus is spreading rapidly across the world, prompting new lockdowns and restrictions in certain countries. In the U.S, it accounts for an increasing number of new infections.
Here are five frequently asked questions and answers about the variant.
How widespread is it?
Delta has been confirmed in 86 countries, including the U.S. It is now the most common variant in India and Britain, where it accounts for more than 90 percent of cases.
The variant was first discovered in the U.S. in March and has spread quickly. The Centers for Disease Control and Prevention (CDC) estimates the variant accounts for about 25 percent of all infections. By comparison, the variant accounted for fewer than 10 percent of cases in early June.
The alpha variant, first found in Britain, has been the most dominant in the U.S. but that will change soon.
"I expect that in the coming weeks it will eclipse the alpha variant," CDC Director Rochelle WalenskyRochelle WalenskyFauci says trick-or-treating this Halloween ok Overnight Health Care — Presented by EMAA — Pfizer requests FDA authorize COVID-19 vaccine for 5 to 11 year olds CDC director urging flu shots ahead of potentially 'severe' season MORE said during a White House briefing Thursday.
Last week, Anthony FauciAnthony FauciFDA advisory panel scheduled to discuss Merck COVID-19 antiviral pill Feehery: Build back bipartisan Overnight Health Care — Presented by The National Council on Mental Wellbeing — Merck asks FDA to authorize five-day COVID-19 treatment MORE, director of the National Institutes of Allergy and Infectious Diseases, said the delta variant is "currently the greatest threat in the U.S. to our attempt to eliminate COVID-19," adding that the proportion of infections caused by the variant is doubling every two weeks.
Who is most at risk of infection?
The delta variant is believed to spread much more easily than both the original strain and the alpha variant of the virus first found in Britain, and may cause much more serious illness.
But the people at highest risk of infection are the adults who are not vaccinated, and children who are not yet eligible to be vaccinated. The risk of serious illness from the delta variant is likely higher for unvaccinated adults, but experts are still concerned that children are at risk.
Former Food and Drug Administration commissioner Scott Gottlieb told CNBC late last month that even though the delta strain isn't necessarily more dangerous to unvaccinated children, the fact that it's more transmissible means there will be more serious cases.
“It’s just math that if more kids get infected, even if the rate of bad outcomes in kids is very low, more kids are going to have bad outcomes because more of them are getting infected,” Gottlieb said.
Walensky on Thursday said the delta variant is the most serious risk to unvaccinated communities.
"Looking across the country we have made incredible progress towards ending the pandemic," Walensky said. "However, looking state by state and county by county, it is clear that communities where people remain unvaccinated are communities that remain vulnerable."
Do the J&J, Moderna and Pfizer vaccines work against it?
All three vaccines currently authorized for use in the U.S. have shown protection against both symptomatic disease and hospitalization from the delta variant, though at slightly reduced levels than against the original variant.
For vaccines that require two doses— that means Pfizer-BioNTech or Moderna in the U.S.— studies have shown both doses are needed to provide the full benefit. One dose of either will not work.
"The science is clear. The best way to protect yourself against the virus, and its variants, is to be fully vaccinated. It works, it's free, it's safe, it's easy and it's convenient," Fauci said Thursday.
A study of real-world data from England showed the Pfizer-BioNTech vaccine was about 88 percent effective at preventing symptomatic disease from the delta variant. Moderna said its vaccine is also highly effective against the delta variant. While the results were based on a lab study, the real-world impact is not likely to differ much.
There has been some concern about the effectiveness of the single-dose Johnson & Johnson vaccine, leading to questions about whether it was appropriate to get a booster of one of the mRNA vaccines.
The company announced late Thursday that its vaccine generated a "strong, persistent" immune response, but the results were not publicly posted yet. The company also said that the immune response produced by the vaccine lasts at least eight months.
Will I need a booster to protect against the variant?
The strong results from the Pfizer-BioNtech and Moderna vaccines seem to indicate that a booster won't be needed, at least to protect against the delta variant. Future mutations may prove more elusive.
The full picture on J&J is still a bit murky. The J&J vaccine is very similar to the one manufactured by AstraZeneca, which proved only about 60 percent effective against the delta variant.
Some recipients of the J&J have taken matters into their own hands by getting doses of either Pfizer-BioNTech or Moderna in the hope it would help boost protection.
Both Walensky and Fauci in recent days have tried to tamp down on this freelancing. The CDC does not endorse mixing vaccines, because there's not enough clinical data to show the benefits outweigh potential risks.
"There's a lot of talk" about vaccine mixing for a booster, Fauci acknowledged at Thursday's White House briefing, but "there's no real fundamental scientific reason to do that right now."
If people decide to go the mixed-dose booster route, public health officials are urging them to do so as part of a clinical trial in order to help gather data.
"The situation right now is that people locally will be making those kinds of decisions, but you should only be making a formal recommendation based on clinical data,” Fauci said.
Do I need to wear a mask?
If you're not vaccinated, the CDC recommendations have not changed, and you never should have stopped wearing a mask indoors or in crowds.
But as restrictions have lifted across the country, masking has largely become optional for everyone because most places rely on the honor system.
Health officials at the state and federal level are grappling with how best to combat the spread of the delta variant, especially with vaccination rates that vary substantially across different areas of the country.
The variant spreads easiest in areas with the lowest vaccine coverage; Walensky said the CDC is monitoring about 1,000 "hot spot" counties with vaccination rates at less than 30 percent. In those areas with high transmission, experts have suggested wearing a mask indoors even if you’re vaccinated.
There likely won't be a political appetite to mandate mask wearing for everyone, at least on the federal level. But there are signs the rules will vary on the local level.
Los Angeles County this week recommended that all people wear masks indoors, even if they're vaccinated. St. Louis County did the same. It's a blunt policy, but without requiring proof of vaccination, local officials said they felt it was the best way to protect everyone.